In this paper,
the fifth of a series dealing with the survey of freshwater gastropods
of the state of Rio de Janeiro, the results of collections carried out
in the Norte Fluminense Mesoregion from 2002 to 2003 are presented and
revealed the occurrence of 19 species: Antillorbis nordestensis; Burnupia sp.; Biomphalaria
tenagophila; Drepanotrema anatinum; Drepanotrema cimex; Drepanotrema
depressissimum; Drepanotrema lucidum; Ferrissia sp.; Gundlachia
ticaga; Gundlachia sp.; Heleobia sp.; Hebetancylus
moricandi; Idiopyrgus sp.; Lymnaea columella; Melanoides
tuberculatus; Physa acuta; Physa marmorata; Pomacea
sordida, and Pomacea sp. Concerning the snail hosts of Schistosoma
mansoni onlyB. tenagophila was found, in contrast with
other previuosly studied mesoregions.No specimens were found harbouring
larval forms of S. mansoni although different kinds of cercariae
had been observed.An account about the current schistosomiasis
transmission sites in this Mesoregion is presented as well.

An intensive and
detailed survey of freshwater snails of the state of Rio de Janeiro has been
performed by the authors since 1997 and the results were published in five
papers (Thiengo et al. 1998, 2001, 2002ab, 2004). Thus, aiming to carry on
that survey collections were made from March, 2002 to September, 2003 in
the following municipalities of the Norte Fluminense Mesoregion: Carapebus,
Conceição de Macabu, Macaé, Quissamã (Macaé Micro-region),
Campos dos Goytacazes, Cardoso Moreira, São Fidélis, São
Francisco de Itabapoana, and São João da Barra (Campos dos
Goytacazes Microregion).

The freshwater
snail species listed include specimens collected by the authors as well as
those in the Collection of the Department of Malacology of Instituto Oswaldo
Cruz. The distribution of the Afro-Asian snail Melanoides tuberculatus and
the snail species of medical and veterinary importance, various kinds of
cercariae and the number of schistosomiasis cases reported to this region
during the last 19 years are also presented.

MATERIALS
AND METHODS

We have adopted
the Brazilian Institute of Geography and Statistic (IBGE 1995) procedures
in dividing the state of Rio de Janeiro into six Mesoregions (Baixadas, Metropolitan,
Centro Fluminense, Sul Fluminense, Norte Fluminense, and Noroeste Fluminense)
and the Center of Information and Data of Rio de Janeiro (CIDE 2001) for
the new municipalities. The Norte Fluminense Mesoregion is 9731 km2,
constituting 22.2% of the state.

The molluscs were
collected from different suitable snail habitats from all 38 districts of
the nine municipalities surveyed. Since at least three different habitats
were investigated in each of the districts, an average of 114 samples was
obtained. Live snails were kept at the laboratory for a month in aquaria
containing dechlorinated tap water and, at the bottom, a thin layer of a
2:1 mixture of screened soil and ground oyster shells as a source of mineral
nutrients. Snails were fed on fresh lettuce leaves. In the meantime all specimens
were exposed to artificial light at five-day intervals to determine possible
infection with trematode larvae. Cercariae were fixed in 70% ethanol, stained
with chloridric carmine, mounted in Canada balsam and subsequently identified
according to Schell (1970).

The 10 larger specimens
of each sample were preserved in Railliet-Henry's fluid after relaxation
in a 0.05% hypnol solution and two of them were dissected under stereomicroscope
for identification.

Samples of taxonomic
importance were deposited at the Malacological Collection of Instituto Oswaldo
Cruz.

The cases of schistosomiasis
reported from 1985 to the first trimester of 2004 were obtained from the
National Health Foundation (Funasa).

The distribution
of B. tenagophila,L. columella, the main intermediate
host of Fasciola hepatica (Linné) in Brazil, as well as that
of the introduced species M. tuberculatus is shown in the Figure.

The highest species
richness occurred in Campos (17 species), São Fidélis (14),
and Macaé (13). On the other hand, in Carapebus and Quissamã only
seven species were found.

Specimens of P. marmorata were
found in all municipalities, but Quissamã whereas those of P. acuta were
found in Campos dos Goytacazes Microregion only.

In contrast to
the other previously studied Mesoregions (Thiengo et al. 2001, 2002a b, 2004) B.
tenagophila was the only schistosomiasis vector found and the most frequent
species, as it was observed in 34 districts.

Although many different
kinds of cercariae had been observed (Table II),
no specimens were found infected with S. mansoni or F. hepatica.
Xiphidiocercariae group (including Ubiquita cercaria and Ornatae cercaria)
were the most frequent type of trematode larvae, as they occurred in the
following species: B. tenagophila, D. cimex, D. depressissimum,
D. lucidum, G. ticaga, L. columella, P. sordida, and Pomacea sp.
The major diversity of cercariae was found in Campos and B. tenagophila showed
the greatest number of mollusc-parasite interactions, followed by D. cimex and Pomacea sp.

Even though no
specific parasitological surveys have been performed by Funasa in the Norte
Fluminense Mesoregion, cases of schistosomiasis were detected in Macaé (one
in 2000; 21 in 2001; 19 in 2002; nine in 2003; and five in 2004), Conceição
de Macabu (14 in 1993; one in 1996 and 2000) and Campos dos Goytacazes (nine
in 1989 and two in 1993).

In relation to
the non-vector planorbid species, D. anatinum was the most common,
followed by D. cimex. In the previously studied mesoregions,
the most frequent species were D. anatinum in the Metropolitana
and Centro Fluminense Mesoregions (Thiengo et al. 2001, 2002a), D. cimex in
the Baixadas Mesoregion (Thiengo et al. 2002b) and D. lucidum in
the Sul Fluminense Mesoregion (Thiengo et al. 2004). The distribution
of A. nordestensis, previously known in 28 municipalities in
the state (Thiengo et al. 1998, Santos et al. 1999, Thiengo et al. 2001,
2002ab, 2004), is now extended to include Campos, Conceição
de Macabu, Macaé, and São Fidélis.

Lymnaea columella shows
wide range in the state and, in Norte Fluminense Mesoregion specimens were
collected from five municipalities and 16 districts.

The Afro-Asian
thiarid M. tuberculatus was found in four municipalities and
seven districts in the northern Norte Fluminense Mesoregion. The current
distribution of that invasive gastropod competitor of planorbid intermediate
hosts of S. mansoni in Brazil had already been reported by our
group (Fernandez et al. 2003). The first record of that species in the country
was in 1967 in Santos, state of São Paulo, and since then it has been
recorded in the Distrito Federal and 17 out of the 26 states from Brazil.

Concerning the
other Prosobranchia, hydrobiid species were found in the all municipalities,
but Conceição de Macabu and Quissamã. Heleobia sp.
was the most frequent species of Hydrobiidae, and Idiopyrgus sp. was
found only in Campos. As in Mesoregion Baixadas the geographical distribution
of hydrobiid species is probably due to favorable environmental conditions
such as the occurrence of many brackish waterbodies, where most specimens
were collected.

Specimens of Pomacea sp.,
collected from eight municipalities, are quite different from those reported
by Thiengo et al. (2002ab, 2004) in Centro Fluminense, Baixadas and Sul Fluminense
Mesoregions. Further morphological and molecular studies are being undertaken
on samples from those regions, in order to identify them.

Among the ancylids G. ticaga occurred
in six municipalities and was the most frequently found species as well as
the previously studied mesoregions. Of the remaining ancylid species, H.
moricandi was reported in the Metropolitana Mesoregion only (Thiengo
et al. 1998), under the name of Gundlachia moricandi (Orbigny, 1837);
specimens of Burnupia sp. were found in the Baixadas and Metropolitana
Mesoregions whereas those of Fer-rissia sp. in all previously studied
Mesoregions.

Due to the limitation
of logistic resources available to Funasa no intensive parasitological surveys
have been done during the last years. Thus the number of positive cases in
the period studied (82 in three municipalities) must be seen as underestimated
information.

With regard to
other trematode, the xiphidiocercariae group was the most frequently larval
type found in the molluscs, corroborating Thiengo et al. (2002a b,
2004).

ACKNOWLEDGEMENTS

To Dr Patricia
Moza (Funasa, RJ) for informing the number of cases of schistosomiasis in
the state.